Went to my favourite yarn shop and bought some undyed wool yarn to combine with the funky one. I think this combination might work out.

The yarn weight isn’t a perfect match – the funky one takes up more space than I expect based on its looks. With the same needles for both, the funky one bulges out a bit. I could try and buy more varieties of gray wool yarn from the internet, until I find a better match, or I can just make do. For the top half of the swatch I tried using 4 mm needles for the funky one and 4.5 mm for the gray one, and that looks pretty even.